The disclosure of Japanese Patent Application No. 11-237511 filed on Aug. 24, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a variable valve apparatus of an internal combustion engine that varies the open-close characteristic of an engine valve by moving a three-dimensional cam in the direction of an axis of the cam, the cam having a cam profile that continuously changes in the direction of the cam axis and a method of varying the open-close characteristic of an engine valve.
2. Description of Related Art
A known variable valve apparatus of an internal combustion engine employing a three-dimensional cam is described in, for example, U.S. Pat. No. 5,924,397. A construction of a detection portion provided in the apparatus for detecting the amount of movement of the camshaft in a direction of an axis thereof is illustrated in FIGS. 5A and 5B. FIG. 5A is a view of the detection portion taken in a direction of the axis of the camshaft. FIG. 5B is a side view of the detection portion taken in a direction indicated by an arrow B in FIG. 5A.
As shown in FIGS. 5A and 5B, an engine camshaft 22 provided with a three-dimensional cam has a pair of detected portions 74 for reference extending linearly in the direction of the axis of the camshaft 22, and a movement amount detected portion 75 for amount of movement extending helically in the direction of the axis. An electromagnetic pickup 76 that generates pulses corresponding to passage of the detected portions 74, 75 is secured to a body of the engine (cylinder head) in the vicinity of the camshaft 22. When the camshaft 22, which is rotated in a direction C in the drawings, is moved in either direction of the axis (leftward or rightward in FIG. 5B), the generation timing of pulses generated by the electromagnetic pickup 76 corresponding to the reference detected portions 74 does not change whereas the generation timing of pulses corresponding to the movement amount detected portion 75 changes. Based on these pulse generation timings, the apparatus accurately detects the amount of movement of the cam (three-dimensional cam). Therefore, precise cam position control (i.e., precise valve characteristic control) can be performed.
In variable valve apparatus employing three-dimensional cams, it is a normal practice to set a camshaft reference position as a positioning reference in the direction of the axis of a camshaft for mounting the camshaft to a cylinder head, or as a detection reference for detecting the amount of movement of the camshaft during operation. This camshaft reference position is also referred to when the electromagnetic pickup 76 and other members are secured to predetermined positions on the cylinder head.
If a base member (cylinder head) to which the electromagnetic pickup 76 is secured and the camshaft where the movement amount detected portion 75 and the like are provided are made of different materials; for example, the cylinder head is formed as a cast aluminum alloy and the camshaft is formed from iron, an increase in the engine temperature causes, in some cases, a positional deviation due to the different rates of thermal expansion of the materials. In such a case, the precision in detecting the amount of movement of the camshaft may decrease, and the control precision related to the valve characteristics determined by the three-dimensional cam, such as the valve-opening angle and the valve lift, may also decrease.
More specifically, even if, during the assembly of the engine, the position of the electromagnetic pickup 76 and the positions of the reference detected portions 74 and the movement amount detected portion 75 are initially adjusted (initialized) based on the camshaft reference position, and the reference position regarding the detection of the amount of movement of the camshaft is initialized, it is difficult to prevent the initialized positions from deviating with increases in the engine temperature, due to different rates of thermal expansion. If detection related to the amount of movement of the camshaft is performed while such a positional deviation exists, there is a possibility that precise control of the valve characteristics through the use of the three-dimensional cam becomes difficult. This possibility is particularly great if the deviation is great.
Accordingly, a variable valve apparatus of an internal combustion engine according to various exemplary embodiments of the invention is capable of realizing more precise valve characteristic control by reducing the error in detection of the amount of movement of a camshaft caused by a difference in the rate of thermal expansion.
The variable valve apparatus of an internal combustion engine for varying an open-close characteristic of an engine valve according to various exemplary embodiments of the invention includes a camshaft that has a plurality of three-dimensional cams whose cam profile continuously changes in a direction of a cam axis and that is supported so as to be rotatable and slidable in the direction of the cam axis relative to a body of the internal combustion engine. The apparatus also includes a movement mechanism that moves the camshaft in a direction of an axis of the camshaft, a camshaft position marker provided in the camshaft, and a camshaft movement amount detector that is provided in the body of the internal combustion engine and that detects the camshaft position marker and detects an amount of movement of the camshaft in the direction of the axis of the camshaft. The camshaft position marker and the camshaft movement amount detector are provided near a reference position that is provided at a predetermined position in a direction of a length of the camshaft.
Therefore, even if the engine body, where the camshaft movement amount detector is provided, and the camshaft, where the camshaft position marker is provided, are made of different materials and therefore have different rates of thermal expansion, the variable valve apparatus is able to reduce the error in detection of the amount of movement of the camshaft caused by the different rates of thermal expansion.
In the variable valve apparatus according to various exemplary embodiments of the invention, the reference position may be provided near a central portion of the camshaft.
The provision of the camshaft movement amount detector near a central portion of the camshaft reduces the distance from the movement amount detector to a farthest three-dimensional cam. Therefore, it becomes possible to reduce the deviation from the initialized position of the movement amount detection means, the deviation being caused by thermal expansion of the camshaft, and to reduce the variation in the amounts of control achieved by the three-dimensional cams in the valve characteristic control.